The current price is £90 from EDF that you pay if you are wrong. British Gas and Swalec want £186 upfront and if you are right they will refund it. As far as a nifty formula used it should be simple enough where power is V*I. Assuming you know the resistance of your load ( I hope in fact it is resistive and not inductive) then you divide the voltage by the resistance to get the current. Taking this actual current and multiplying it by voltage you get the actual power consumption. This is much more accurate as the clamp on ammeter may or not be accurate. Also you use the pulses from the customers meter ( only on the newer ones) Which can also have an inductive error. I am glad your meters have such a high accuracy. I have seen, as I mentioned previously, 100% are over 10% high. Guess we should all move to where you are. John

I recently challenged my electrical supplier on the accuracy of their meter readings. I must admit they tried everything to make me feel the fool and when that did not work advised me of the cost of having someone come out and test my meter if I was wrong. I went to Energy Watch and they got their customer complaints section involved and they then sent EON to do a Meter Accuracy Test instead of installing a check meter. The upshot was my meter was 24.95% reading too high. I have received an apology letter and then a rebate of the overpaid amounts. I have been doing power measurements on RF Systems for over 30 years so therefore I have both the equipment and the ability to test my meters. One of the "tricks" the suppliers like to try is to have you list the equipment that you have in your home and then they will inform you based on the current ratings of the equipment that their readings are accurate. The current ratings of the equipment in your homes is not the current draw of the individual equipment but rather a nominal indication of the current rating or maximum draw of the equiipment. For example many 1KW heater only draw 800 watts of power and if you were using this for a test of your utilisation you would not be accurate. The best test is to have a fixed resistive load placed on your system for a set period of time to see if the meter is really accurate. In my case I used a 52.5ohm load capable of handling 2500 watts. This load would reach 1kw in 54.7 minutes. So if I had set the meter to where it just clicked over in a unit that did not have a tenths reading. It would click over again in 54.7 minutes Since finding the defective meter and receiving my refund I have checked an additional 10 meters in my area and have found, not the 2% as told to me by my supplier but that 100% of the meters have been from 10 - 27% reading high. I can not reccomend enough to anyone with a question about their readings being high to get them independently tested. The reason I say independent is that the replacement meter arrived from my supplier and it is also 10% high. So I begin the procedure once again with my supplier. I will update as the Saga continues. John